Those doing the puzzle are challenged to find out which of the four cups — from 4 to 5, 7 and 9 — will get served first.

A picture of the brainteaser was posted on Twitter earlier this week, and thousands of people have attempted to solve it, so can you get it right?

It’s much harder than you think, with some thinking the cups would “all get it at the same time”, and others still getting it wrong despite meticulously studying the shape of the faucets and square containers.

While one frustrated bloke simply tweeted: “I’m out”. If you think you’ve cracked it, read on for the answer ...